ViewBinding
的作用:代替findViewById
,还可以保证空安全和类型安全。
基本原理:会为每一个布局xml文件生成一个视图绑定类,类名称是布局文件名转化为UpperCamelCase + Binding。如布局文件为activity_main,那么将会生成一个类,类名为ActivityMainBinding。通过生成对象根节点对象就可以找到对应的Id。
基本用法:
在build.gradle
添加如下配置
android {
...
viewBinding {
enabled = true
}
}
对于不需要生成绑定类的布局xml文件,在根节点添加下面的属性tools:viewBindingIgnore="true"
。
在Activity中使用
布局文件
<-- activity_main.xml -->
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:id="@+id/btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/tv"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constraintTop_toBottomOf="@id/btn"
android:layout_marginTop="20dp"
android:textSize="20sp"
android:text="hello view"
android:gravity="center"/>
</androidx.constraintlayout.widget.ConstraintLayout>
程序中:
class MainActivity : AppCompatActivity() {
private lateinit var binding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
val view = binding.root
setContentView(view)
binding.btn.setOnClickListener {
binding.tv.text = "Binding View"
}
}
}
在Fragment中使用
主布局里面的fragment标签必须要有id。Fragment中的代码如下:
class TestFragment:Fragment() {
private var _binding : TestFrameBinding? = null
private val binding get() = _binding!!
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = TestFrameBinding.inflate(inflater,container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
binding.frameBtn.setOnClickListener {
binding.frameBtn.text = "clicked"
}
}
override fun onDestroy() {
super.onDestroy()
_binding = null
}
}
RecyclerView中
class TestAdapter(list: List<String>) : RecyclerView.Adapter<TestAdapter.ViewHolder>() {
private var mList: List<String> = list
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val binding = ItemTestBinding.inflate(LayoutInflater.from(parent.context), parent, false)
return ViewHolder(binding)
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder.tvItem.text = "Adapter"
}
override fun getItemCount() = mList.size
class ViewHolder(binding: ItemTestBinding) : RecyclerView.ViewHolder(binding.root) {
var tvItem: TextView = binding.tvItem
}
}
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